Spectroscopy is widely used in physical and analytical chemistry as well as in industrial applications for the identification of substances through the spectra emitted from or absorbed by them. Spectroscopy apparatus in the visible wavelength generally employs a diffractive grating or a dispersive prism together with a photo detector array, such as a CCD or CMOS image sensor. While in the near infrared (NIR) to infrared (IR) wavelength, spectroscopic analysis is generally performed with a Michelson interferometer (a so-called Fourier transform spectrograph) and a single element photo detector due to the lack of appropriate high-sensitivity and low-cost array detectors. The Fourier transform spectrograph suffers from a relatively low scanning speed and long-term stability and repeatability problems due to the existence of mechanical moving parts. There thus exists a need for an improved NIR or IR spectroscopy apparatus which solves the above mentioned problems.